RCDs with a self-test capability are available on the market. These devices however are usually either large and expensive or only test a part of the functionality of the entire device. Mostly mechanical parts as contacts, trip-units, mechanisms are not tested. The most reliable known self-test RCD has a double mechanism and bridges the first RCD part by a second RCD while the first is tested including the contacts and mechanical parts. However this solution, as e.g. described in the European patent application EP-A-1 916 691 is an expensive solution that requires a large amount of space.
A further prior art circuit breaker is known from U.S. Patent Application Publication No. 2002/181175, which discloses a digital fault interrupter (or Ground fault circuit interrupter GCFI) with self-testing capabilities. A controller is provided which periodically opens the contacts of the circuit breaker, and monitors a voltage over the load connected to the circuit breaker to check that the contacts have opened. However, further parts or functions of the GCFI are not tested.